/**
*      author: Y_Yao
*      created: 2025-02-22 13:02:41
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
int n,m;

void solve()
{
    cin >> n >> m;
    int ans = 0;
    if(2 * n <= m)
    {
        ans += n;
        m -= 2 * n;
        n = 0;
        ans += m / 4;
    }
    else 
    {
        ans += m / 2;
    }
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}